Characteristics of the turbulence intermittency and its influence on the turbulent transport in the semi -arid region of the Loess Plateau

In this study, observational data from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) in July 2008 were used to analyze the characteristics of the turbulence intermittency and its influence on the land-atmosphere turbulent transport over the complex terrain of the semi-arid region of the Loess Plateau in summer. Using the Hilbert-Huang transform (HHT), the local intermittent strength of turbulence (LIST) was calculated based on pure dynamics through an automated algorithm to characterize the turbulence intermittency in this region. But LIST misjudged the actual turbulence intermittency under the condition of weak wind and strong radiation. The thermal effects cannot be ignored in this situation and a thermodynamic intermittency correction factor LISTThermal is suggested to modify LIST. Then a new intermittent strength index LISTReviseis proposed, which is assumed to be the weighted average of LIST and LISTThermal according to the stability parameter z/L. LIST (LISTThermal) is closely related to the near-surface wind-speed (sensible heat flux). Most misjudgments of LIST to turbulence intermittency are corrected, and LISTRevise is more consistent with the general diurnal variation of turbulence intermittency. There are overestimations in turbulent standard deviations and fluxes calculated by conventional eddy covariance (EC) method due to sub-mesoscale motions and turbulence intermittency, producing inaccurate quantifications of turbulent mixing and transport in the planetary boundary layer parameterization schemes. After eliminating the influence of it, the relationship between the normalized standard deviations of different meteorological variables and z/L is more consistent with the Monin-Obukhov similarity rule under stable and unstable stratification.

Automated summary

Observational data from SACOL in July 2008 were used to analyze turbulence intermittency and its influence on land-atmosphere turbulent transport on the Loess Plateau. A new intermittent strength index LISTRevise was proposed to correct misjudgments of turbulence intermittency and better capture the diurnal variation. The study highlights the importance of thermodynamic intermittency correction in accurately quantifying turbulent mixing and transport in planetary boundary layer parameterization schemes.